This invention relates to a device, apparatus or assembly for impeding the flow of liquid cargo such as petroleum from a storage compartment of a water-traveling vessel such as a tanker upon damage to a hull of the tanker. This invention also relates to a method for minimizing spillage of the liquid cargo into the environment from a damaged compartment of a water-traveling vessel.
Bulk liquid cargo such as petroleum is generally transported in sea-going vessels such as freighters or tankers having a single walled hull defining a hold. Even though the hold of such a ship is usually subdivided into a plurality of storage compartments, those compartments are nevertheless so large that, should an accident occur and the hull of the vessel become perforated or fractured, a great quantity of petroleum or other liquid cargo is likely to spill into the environment. The great ecological damage resulting from such a spill has been brought to the public's attention through several well publicized incidents.
In the case of a shipwrecked or stranded ship, where the hull of the ship has been perforated and a storage compartment bearing liquid cargo is in communication with the sea, the waves act to pump oil from the storage compartment and, over the course of several hours, a large amount of the cargo may be spilled out onto the water.
One previously proposed solution to the problem of minimizing the potential damage due to oil spills is to use a double hull. Such a solution has at least two substantial drawbacks: cost and ineffectiveness. The cost of equipping new tankers with a double hull is obvious. Moreover, it would be practically impossible to retrofit existing tankers with a double hull at any reasonable cost.
A double hull may be ineffective in many situations because whatever can pierce or fracture a steel plate three-quarters of an inch thick could well be sufficiently forceful to pierce a second steel plate spaced a short distance inwardly from the outer hull wall.
An alternative solution to the double hull is the provision of a flexible liner inside each compartment of a petroleum carrying vessel. Such a solution is certainly less expensive than double hulls and can be used in retrofitting existing vessels.
Impermeable flexible liners or bladders are disclosed in U.S. Pat. No. 4,230,061 to Roberts et al. and U.S. Pat. No. 3,844,239 to McLaughlin et al. Roberts et al. more particularly discloses a petroleum bearing bladder of a woven polyester material coated with a liquid and gas impervious film in the form of a silicone rubber elastomer. Advantages of such a flexible inner liner include easy installation in existing vessels and easy removal to enable repairs on the inner side of the ship's hull. Disadvantages of the liner of Roberts et al. is that it does not conform to the inner wall of the hull and thus reduces the amount of payload. In addition, because the liner must continually support the liquid cargo, the liner is subject to considerable stresses during periods of normal, non-emergency use. Such continual stresses greatly weaken the fabric material and may result, in emergency situations, in failure which otherwise would not have occurred but for the fatigue stressing of the liner material.
McLaughlin et al. is directed to an ejection piping system in which each storage compartment of a tanker is connected via a conduit to an empty space. Each compartment is additionally lined with an impermeable, elastomeric tailored lining releasably fixed to the inner walls of the respective compartment. Upon a deformation of the walls of the storage compartment due to a collision, the liner is released and flexes inwardly to eject the liquid payload, e.g., crude oil, through the conduit to empty space.
The solution of McLaughlin et al. avoids the disadvantages of payload reduction and liner stressing, inasmuch as the liner is, in at least one specific embodiment, disposed in contact with the inner surface of the storage compartment, including the hull. In the event of a collision, the liner separates from the compartment surface. A disadvantage of such a system is that the liner, in being located against the hull, most probably will be torn, shredded or pierced by the same force which opens a hole in the side of the vessel.
The use of flexible liners to contain liquid bulk materials has also been proposed with respect to the transport of cold liquified gases. U.S. Pat. Nos. 3,883,591 and 3,827,136 to Yamamoto, U.S. Pat. No. 3,272,373 to Alleaume et al. and U.S. Pat. No. 2,994,452 to Morrison all relate to liquified gas storage tanks including a membranous lining. More particularly, both patents to Yamamoto show a low temperature liquified gas tank having an inner membrane provided inside a rigid outer vessel with the interposition of a heat insulating layer. The tank is constructed so that the liner conforms as much as possible to the outer vessel.
Alleaume et al. describes an impermeable inner membrane which contains a cold liquified substance and is in contact with a hull of a ship. The membrane takes the form of a large bag held at its neck at an opening in the top of a storage compartment in which the bag is placed. In Several embodiments disclosed in Alleaume et al., two bags are placed within a storage compartment, one bag inside the other, the bags being separated by pressurized gas or cellular material.
Morrison involves a storage facility including a cylindrical outer tank made of steel, an intermediate insulating layer of balsa wood and a inner bag or lining made of a woven glass fiber impregnated and coated with synthetic resin material. A plurality of flexible supporting straps or hangers suspends the bag from the roof of the steel tank.
In solving other problems, including that of transporting two different kinds of fluidic materials in the same storage compartment of a ship so that the materials do not mix or come into contact with one another, U.S. Pat. No. 4,347,798 to Gallagher discloses an expandable bag disposed at the bottom of a storage compartment. The expandable bag may be partially or completely filled with a buffer fluid to protect cargo in the storage compartment from a penetration through the bottom of the compartment. The expandable bag is made of a material which is impervious to liquid cargo contained in the storage compartment.
Another solution to minimizing the spillage of petroleum from a damaged tanker is to provide a floating flexible structure into which the petroleum may be pumped from one or more damaged compartments of the tanker. As disclosed in U.S. Pat. No. 4,373,462 to Fish, such a structure may then be towed away for disposal of the oil. Fish more specifically sets forth a towable tank comprising four elongate pieces fixed to each other by side seams and upper and lower seams to form a receptacle. In addition, clamps are applied to the pieces at the front and the rear of the assembly.
U.S. Pat. No. 4,227,477 to Preus also discloses an inflatable, flexible, towable container for receiving petroleum from a damaged vessel and transporting the petroleum to dockside or to another vessel. The inflatable container is provided along its sides and, in some embodiments, along its entire periphery with gas-inflatable buffer or bumper tubes for protecting the skin of the container from rupturing due to collisions with floating wreckage, jetties, etc.
Two other patents which disclose flexible floating tanks for conveying liquids are U.S. Pat. No. 3,952,679 to Grihange and U.S. Pat. No. 3,735,721 to Leguijt. A floating tank in accordance with the disclosure of Grihange comprises a pair of elongate tanks disposed side by side and joined to one another by a flexible linking harness. The tanks are internally divided by bulkheads and have oblique forward ends. The tanks' shapes are maintained by inflating gas.
Leguijt discloses an oil storage system comprising rectangular basin divided by partitions into a plurality of compartments each containing an envelope floating in water and in turn containing oil. The envelopes are rectangular when empty and made of impregnated nylon fabric.
Proposing another solution to the problem of confining oil in a tanker upon rupture of the hull of the tanker in an accident, U.S. Pat. No. 2,699,912 to Wilson, Jr. discloses an apparatus including a cup shaped inner barrier and an inverted outer barrier, both comprising panels made of form-sustaining but liquid-tight material sealingly secured to the walls of one or more compartments of a ship's hull. Should the hull be ruptured, the panels deform without rupturing and cooperate with each other to form a seal against the escape of the oil.